Data is collected from floor sensors and analyzed. The sensors pick up the vibration waves that pass through the floor when someone takes a step. By examining these waves, Noh said she can figure out how fast someone is moving, how much they weigh and their shoe type.

"The waveform actually looks different depending on how you walk, whether you're wearing high heels, etc.," she said. High heels produce higher frequency vibration waves than tennis shoes. When a person is turning, they place more weight on one foot, producing a footstep wave that is noticeably higher than the others.

The sensors also can be used to find people. Through using three sensors in different locations, footstep waves arrive at different times with different amplitudes. The information can be triangulated to pinpoint a person's exact location.

Businesses already have expressed interest in using this technology for security purposes. Noh said another application could involve retailers combining sensor data with the information from clothing tags to determine what items customers take into dressing rooms.

With enough sensors, Noh said hundreds of people can be tracked simultaneously.

In large areas such as shopping malls, sensors use the floor's general vibration level to estimate the number of people and what types of activities are occurring. These factors influence a building's electricity and energy use making sensors a nonintrusive way to monitor energy consumption.

In addition to Noh and Zhang, CMU contributors include Ph.D. students Chandrayee Basu and Shijia Pan and undergraduate Amelie Marie Bonde (CS'14).

"Vibration analysis can be applied to floors, buildings, trains and different things. Vibration is everywhere," Noh said.